Advances in Plant-Atmospheric Interactions

Abstract

Water is the main driver of ecosystem productivity in most terrestrial ecosystems worldwide. The predicted increase in rainfall variability and extreme climatic events under future climate conditions are therefore anticipated to strongly affect plant and ecosystem functioning. As 55–70% of terrestrial evapotranspirational water loss is directly controlled by plants (Schlesinger & Jasechko, 2014), transpiration comprises the largest water flux from Earth's continents, creating a dominant force in the global water cycle. Plant transpiration is controlled by the availability of soil water and root uptake from different soil depths, transport velocities in the xylem, and transpirational water loss through stomates during photosynthesis driven by the atmospheric demand (leaf‐to‐air water vapour deficit), and the species‐specific sensitivity of stomatal control of water loss. In turn, plants modulate the available water resources in ecosystems by modifying interception, rain water infiltration, soil evaporation and groundwater recharge (e.g. Rodriguez‐Iturbe, 2000). Different species with diverse rooting systems and depths have different effects on soil water infiltration, as well as different capacities to utilize various soil water pools (Jackson et al., 2000). Since the 1980s, experimental evidence has ascertained the pivotal role of plant roots for soil water redistribution, such as hydraulic lift of deep water sources into shallower and dryer soil layers (Caldwell, 1987), thereby promoting or buffering competition for this highly valuable resource within plant communities. In spite of these insights, quantification of dynamic soil–vegetation feedbacks within the water cycle remains a major challenge. Progress has partially been hampered by the fact that blue (abiotic, e.g. stream, run off) and green (biotic, e.g. vegetation water losses) water flows were mostly investigated separately in different disciplines. Given that extreme events such as floods and droughts are predicted to increase in frequency for many regions, dynamic species‐specific responses in root water uptake to changing available water pools play a pivotal role in the understanding of the ecosystem water balance and functioning. In this regard, more interdisciplinary approaches, bridging hydrology, ecophysiology and atmospheric science are needed. In this issue of New Phytologist, Volkmann et al. (pp. 839–849) were able to investigate this hidden part of the soil–vegetation interaction. Volkmann et al. quantified rapid dynamics of rainwater infiltration within the rooting zone of mixed and monoculture tree saplings. The consecutive responses in plant root water uptake and utilization of a rain pulse revealed high species‐specificities not in line with the distribution of roots within the soil profile. Furthermore, a novel dimension of temporal and spatial resolution in soil water flow processes was achieved, utilizing newly developed stable isotope‐based methods.